Dihydroxy terminated triblock copolymer surfactants are known having the general structure H-(E).sub.a (P).sub.b (E).sub.a -OH wherein E represents oxyethylene and P represents oxypropylene. Such nonionic surfactants are commercially available e.g. Pluronic.TM. surfactants.
U.S. Pat. No. 4,072,704 describes the preparation of polyoxyalkylene block copolymer surfactants by reacting individual blocks of polymers and copolymers of alkylene oxides with formaldehyde or a dialkyl carbonate. For example, the surfactants can contain polyoxyethylene and polyoxypropylene polymers linked by formal or carbonate groups.